The present invention relates to cochlear implants, and more particularly to an auto-referencing mixed-mode phase locked loop for audio playback applications, such as occurs when performing audio streaming diagnostics relative to the performance of a bionic ear implant.
A new generation of cochlear implants, commonly referred to as a “bionic ear” implant, has recently been introduced to the cochlear implant community. A representative bionic ear implant is the CII Bionic Ear™ cochlear implant system introduced by Advanced Bionics Corporation, of Sylmar California. A bionic ear implant is capable of delivering electrical stimulation to a patient at rates and resolutions which surpass that of conventional cochlear implants.
With any cochlear implant, there is a continual need to know how the implant is functioning and what the patient using the cochlear implant is hearing. That is, patients may report hearing “noise” or “distortion” in a particular channel, and may use such terms as “cracking”, “popping” “tickling”, “gurgling”, “rattling” etc. to describe such noise. It would thus be helpful if the clinician or other interested parties, e.g., parents or teachers of young children who have been fitted with a cochlear implant, could actually “hear” what the patient is hearing. Disadvantageously, there has not been a diagnostic tool available that has allowed such listening.
In order to “listen in” to what a cochlear implant patient may be hearing, it is necessary to process an asynchronous stream of digital audio samples that arrive at a receiver location at a consistent, but unknown, average rate. Once the stream of asynchronous audio samples are received, there is a need for a way of extracting the average sample rate, generating a local clock at the average frequency, and re-synchronizing the incoming audio samples to that clock. With such re-synchronized clock, it would then be possible to recreate the stream of audio data so that one can listen to it, or analyze it for other diagnostic purposes.